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  • 1. Nuclear Chemistry Chapter 23
  • 2. RadioactivityRadioactivity • One of the pieces of evidence for theOne of the pieces of evidence for the fact that atoms are made of smallerfact that atoms are made of smaller particles came from the work ofparticles came from the work of Marie CurieMarie Curie (1876-1934).(1876-1934). • She discoveredShe discovered radioactivityradioactivity,, the spontaneous disintegration ofthe spontaneous disintegration of some elements into smaller pieces.some elements into smaller pieces.
  • 3. Nuclear Reactions vs.Nuclear Reactions vs. Normal Chemical ChangesNormal Chemical Changes • Nuclear reactions involve the nucleusNuclear reactions involve the nucleus • The nucleus opens, and protons andThe nucleus opens, and protons and neutrons are rearrangedneutrons are rearranged • The opening of the nucleus releases aThe opening of the nucleus releases a tremendous amount of energy that holdstremendous amount of energy that holds the nucleus together – calledthe nucleus together – called bindingbinding energyenergy • ““Normal” Chemical Reactions involveNormal” Chemical Reactions involve electronselectrons, not protons and neutrons, not protons and neutrons
  • 4. Types of RadiationTypes of Radiation e0 1− He4 2 • Alpha (Alpha (άά) – a positively) – a positively charged (+2) helium isotopecharged (+2) helium isotope -- we usually ignore the charge because itwe usually ignore the charge because it involves electrons, not protons and neutronsinvolves electrons, not protons and neutrons •Beta (Beta (ββ) – an electron) – an electron •Gamma (Gamma (γγ) – pure energy;) – pure energy; called a ray rather than acalled a ray rather than a particleparticle γ0 0
  • 5. Other Nuclear ParticlesOther Nuclear Particles e0 1+ n1 0• NeutronNeutron • Positron – a positivePositron – a positive electronelectron •Proton – usually referred toProton – usually referred to as hydrogen-1as hydrogen-1 •Any other elemental isotopeAny other elemental isotope H1 1
  • 6. Penetrating AbilityPenetrating Ability
  • 7. Geiger-Müller Counter 23.7
  • 8. Geiger Counter • Used to detect radioactive substances
  • 9. XA Z Mass Number Atomic Number Element Symbol Atomic number (Z) = number of protons in nucleus Mass number (A) = number of protons + number of neutrons = atomic number (Z) + number of neutrons A Z 1 p1 1 H1or proton 1 n0 neutron 0 e-1 0 β-1or electron 0 e+1 0 β+1or positron 4 He2 4 α2or α particle 1 1 1 0 0 -1 0 +1 4 2 23.1
  • 10. Balancing Nuclear Equations 1. Conserve mass number (A). The sum of protons plus neutrons in the products must equal the sum of protons plus neutrons in the reactants. 1 n0U235 92 + Cs138 55 Rb96 37 1 n0+ + 2 235 + 1 = 138 + 96 + 2x1 2. Conserve atomic number (Z) or nuclear charge. The sum of nuclear charges in the products must equal the sum of nuclear charges in the reactants. 1 n0U235 92 + Cs138 55 Rb96 37 1 n0+ + 2 92 + 0 = 55 + 37 + 2x0 23.1
  • 11. 212 Po decays by alpha emission. Write the balanced nuclear equation for the decay of 212 Po. 4 He2 4 α2oralpha particle - 212 Po 4 He + A X84 2 Z 212 = 4 + A A = 208 84 = 2 + Z Z = 82 212 Po 4 He + 208 Pb84 2 82 23.1
  • 12. Nuclear Stability and Radioactive Decay Beta decay 14 C 14 N + 0 β + ν6 7 -1 40 K 40 Ca + 0 β + ν19 20 -1 1 n 1 p + 0 β + ν0 1 -1 Decrease # of neutrons by 1 Increase # of protons by 1 Positron decay 11 C 11 B + 0 β + ν6 5 +1 38 K 38 Ar + 0 β + ν19 18 +1 1 p 1 n + 0 β + ν1 0 +1 Increase # of neutrons by 1 Decrease # of protons by 1 ν and ν have A = 0 and Z = 0 23.2
  • 13. Electron capture decay Increase # of neutrons by 1 Decrease # of protons by 1 Nuclear Stability and Radioactive Decay 37 Ar + 0 e 37 Cl + ν18 17-1 55 Fe + 0 e 55 Mn + ν26 25-1 1 p + 0 e 1 n + ν1 0-1 Alpha decay Decrease # of neutrons by 2 Decrease # of protons by 2 212 Po 4 He + 208 Pb84 2 82 Spontaneous fission 252 Cf 2125 In + 21 n98 49 0 23.2
  • 14. Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He ? + 1 n 5 2 0
  • 15. Learning Check What radioactive isotope is produced in the following bombardment of boron? 10 B + 4 He 13 N + 1 n 5 2 7 0
  • 16. Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60. 6060 CoCo 00 ee ++ 6060 NiNi 2727 -1-1 2828
  • 17. Artificial Nuclear ReactionsArtificial Nuclear Reactions New elements or new isotopes of known elementsNew elements or new isotopes of known elements are produced by bombarding an atom with aare produced by bombarding an atom with a subatomic particle such as a proton or neutronsubatomic particle such as a proton or neutron -- or even a much heavier particle such as-- or even a much heavier particle such as 44 HeHe andand 1111 B.B. Reactions using neutrons are calledReactions using neutrons are called γγ reactionsreactions because abecause a γγ ray is usuallyray is usually emitted.emitted. Radioisotopes used in medicine are often made byRadioisotopes used in medicine are often made by γγ reactions.reactions.
  • 18. Artificial Nuclear ReactionsArtificial Nuclear Reactions Example of aExample of a γγ reactionreaction is productionis production of radioactiveof radioactive 3131 P for use in studies of PP for use in studies of P uptake in the body.uptake in the body. 3131 1515P +P + 11 00n --->n ---> 3232 1515P +P + γγ
  • 19. Transuranium ElementsTransuranium Elements Elements beyond 92Elements beyond 92 (transuranium)(transuranium) mademade starting with anstarting with an γγ reactionreaction 238238 9292U +U + 11 00n --->n ---> 239239 9292U +U + γγ 239239 9292UU --->---> 239239 9393Np +Np + 00 -1-1ββ 239239 9393NpNp --->---> 239239 9494Pu +Pu + 00 -1-1ββ
  • 20. Nuclear Stability • Certain numbers of neutrons and protons are extra stable • n or p = 2, 8, 20, 50, 82 and 126 • Like extra stable numbers of electrons in noble gases (e- = 2, 10, 18, 36, 54 and 86) • Nuclei with even numbers of both protons and neutrons are more stable than those with odd numbers of neutron and protons • All isotopes of the elements with atomic numbers higher than 83 are radioactive • All isotopes of Tc and Pm are radioactive 23.2
  • 21. Band of StabilityBand of Stability and Radioactiveand Radioactive DecayDecay
  • 22. Half-LifeHalf-Life • HALF-LIFEHALF-LIFE is the time that it takes foris the time that it takes for 1/2 a sample to decompose.1/2 a sample to decompose. • The rate of a nuclear transformationThe rate of a nuclear transformation depends only on the “reactant”depends only on the “reactant” concentration.concentration.
  • 23. Half-LifeHalf-Life Decay of 20.0 mg ofDecay of 20.0 mg of 1515 O. What remains after 3 half-lives?O. What remains after 3 half-lives? After 5 half-lives?After 5 half-lives?
  • 24. Kinetics of Radioactive DecayKinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234 After 3.6 days > 25 gramsAfter 3.6 days > 25 grams After 7.2 days > 12.5 gramsAfter 7.2 days > 12.5 grams After 10.8 days > 6.25 gramsAfter 10.8 days > 6.25 grams
  • 25. Kinetics of Radioactive Decay A daughter rate = - ∆A ∆t A = A0e(-kt) lnA = lnA0 - kt A = the amount of atoms at time t A0 = the amount of atoms at time t = 0 k is the decay constant (sometimes called λ) Ln 2 = k 23.3 t½ 0.693 = k t½
  • 26. Radiocarbon Dating 14 N + 1 n 14 C + 1 H7 160 14 C 14 N + 0 β + ν6 7 -1 t½ = 5730 years Uranium-238 Dating 238 U 206 Pb + 8 4 α + 6 0 β92 -182 2 t½ = 4.51 x 109 years 23.3
  • 27. Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 31 hours?
  • 28. 23.8 Biological Effects of Radiation Radiation absorbed dose (rad) 1 rad = 1 x 10-5 J/g of material Roentgen equivalent for man (rem) 1 rem = 1 rad x Q Quality Factor γ-ray = 1 β = 1 α = 20
  • 29. Effects of RadiationEffects of Radiation
  • 30. Nuclear FissionNuclear Fission Fission is the splitting of atomsFission is the splitting of atoms These are usually very large, so that they are not as stableThese are usually very large, so that they are not as stable Fission chain has three general steps:Fission chain has three general steps: 1.1. Initiation.Initiation. Reaction of a single atom starts theReaction of a single atom starts the chain (e.g.,chain (e.g., 235235 U + neutron)U + neutron) 2.2. PropagationPropagation.. 236236 U fission releases neutrons thatU fission releases neutrons that initiate other fissionsinitiate other fissions 3.3. TerminationTermination..
  • 31. Nuclear FissionNuclear Fission
  • 32. Nuclear Fission 23.5 235 U + 1 n 90 Sr + 143 Xe + 31 n + Energy92 54380 0 Energy = [mass 235 U + mass n – (mass 90 Sr + mass 143 Xe + 3 x mass n )] x c2 Energy = 3.3 x 10-11 J per 235 U = 2.0 x 1013 J per mole 235 U Combustion of 1 ton of coal = 5 x 107 J
  • 33. Representation of a fission process.
  • 34. Mass DefectMass Defect • Some of the mass can be converted intoSome of the mass can be converted into energyenergy • Shown by a very famous equation!Shown by a very famous equation! E=mcE=mc22 EnergyEnergy MassMass Speed of lightSpeed of light
  • 35. Nuclear binding energy (BE) is the energy required to break up a nucleus into its component protons and neutrons. BE + 19 F 91 p + 101 n9 1 0 BE = 9 x (p mass) + 10 x (n mass) – 19 F mass E = mc2 BE (amu) = 9 x 1.007825 + 10 x 1.008665 – 18.9984 BE = 0.1587 amu 1 amu = 1.49 x 10-10 J Converts amu to kg and multiplies by c2 BE = 2.37 x 10-11 J binding energy per nucleon = binding energy number of nucleons = 2.37 x 10-11 J 19 nucleons = 1.25 x 10-12 J 23.2
  • 36. Nuclear binding energy per nucleon vs Mass number nuclear binding energy nucleon nuclear stability 23.2
  • 37. Nuclear Fission 23.5 Nuclear chain reaction is a self-sustaining sequence of nuclear fission reactions. The minimum mass of fissionable material required to generate a self-sustaining nuclear chain reaction is the critical mass. Non-critical Critical
  • 38. Nuclear Fission & POWERNuclear Fission & POWER • Currently about 103Currently about 103 nuclear power plants innuclear power plants in the U.S. and about 435the U.S. and about 435 worldwide.worldwide. • 17% of the world’s17% of the world’s energy comes fromenergy comes from nuclear.nuclear.
  • 39. Diagram of a nuclear power plant
  • 40. Annual Waste Production 23.5 35,000 tons SO2 4.5 x 106 tons CO2 1,000 MW coal-fired power plant 3.5 x 106 ft3 ash 1,000 MW nuclear power plant 70 ft3 vitrified waste Nuclear Fission
  • 41. Nuclear Fusion Fusion small nuclei combine 2 H + 3 H 4 He + 1 n + 1 1 2 0 Occurs in the sun and other stars Energy
  • 42. Nuclear Fusion Fusion • Excessive heat can not be contained • Attempts at “cold” fusion have FAILED. • “Hot” fusion is difficult to contain
  • 43. 23.7 Radioisotopes in Medicine • 1 out of every 3 hospital patients will undergo a nuclear medicine procedure • 24 Na, t½ = 14.8 hr, β emitter, blood-flow tracer • 131 I, t½ = 14.8 hr, β emitter, thyroid gland activity • 123 I, t½ = 13.3 hr, γ−ray emitter, brain imaging • 18 F, t½ = 1.8 hr, β+ emitter, positron emission tomography • 99m Tc, t½ = 6 hr, γ−ray emitter, imaging agent Brain images with 123 I-labeled compound
  • 44. Chemistry In Action: Food Irradiation Dosage Effect Up to 100 kilorad Inhibits sprouting of potatoes, onions, garlics. Inactivates trichinae in pork. Kills or prevents insects from reproducing in grains, fruits, and vegetables. 100 – 1000 kilorads Delays spoilage of meat poultry and fish. Reduces salmonella. Extends shelf life of some fruit. 1000 to 10,000 kilorads Sterilizes meat, poultry and fish. Kills insects and microorganisms in spices and seasoning.